peavey400bh

[robgrif]

hi all
this question probably has a solution posted but i am unable to find
it
my 400 bh peavey produces 50 volts dc at the speaker output
not good i am sure any thoughts on probable cause and remedy
please direct me to a solution if one exists already in the forum
no visible signs of damage on board
thanks in advance
robgrif

[Enzo]

400BH is only the power amp panel on the rear of your amp. What the front says probably doesn;t matter considering your symptom - a blown power amp, but it would be nice to know what model amp you have.

DC on the output? Look for shorted output transistors, open or shorted driver trasnsistors, and predriver transistors. And check all the power resistors for opens. There are some small 47 ohm resistors associated with the predrivers, check for opens.

make sure the Voltgae AMp transistor is not open.

try a new TL074 in the socket.

Do not connect a speaker until you get rid of the DC.

ANd do a search on this forum for 400BH, we have discussed and troubleshooted - troubleshot? - this board a number of times.

[robgrif]

Hi Enzo
as per your request about the amplifier it is a 1980 peavey mark 111 bass amplifier showing DC at speaker output of 37 volts
it uses the 400BH board
now on to the good news after reading your speedy reply (thanks) and a couple of posts about testing transistors and resistors etc. and found everything in order as far as I could tell I switched out the op amp tl074cn as suggested and the beast roared back to life
kudos to you Enzo you are amazing
the only thing I notice now is on power down is it sounds as if some small animal is inside
as it sort if meows for lack of a better term on power off
to recap
amp powers up
had approx 37 DC volts at speaker output 400BH board
changed the op amp tl074cn with new one same number (Enzo's suggestion)
amplifier now works again
thanks again Enzo
this is a great forum with great people willing to help
regards
Robgrif





l

[Gtr_tech]

You mean TL074 right? Anyway....if its a DC coupled amp any of several things can cause the output transistors to put rail voltage on the output. They just "do as they're told". As you found, an op amp that's shorted its output to a rail is one cause.

[robgrif]

You mean TL074 right? Anyway....if its a DC coupled amp any of several things can cause the output transistors to put rail voltage on the output. They just "do as they're told". As you found, an op amp that's shorted its output to a rail is one cause.

thanks for the info
it is quite a learning curve for a layman like myself I appreciate the help from the forum
Any thoughts on the cause of the meowy sound in the speaker when the amp is turned off
very annoying sound to say the least and quite loud
faulty capacitor somewhere perhaps?